In medical fields, medical adhesive tapes such as surgical tapes, plasters (first-aid plasters), etc., are applied to adhere medical appliances, rolled bandages, wound dressings, transdermal absorbents, etc., to the skin.
The adhesive tape is composed of an adhesive which is coated on a backing layer. Such an adhesive tape should have adhesion suitable for firmly adhering the medical appliances or dressing materials to the skin and subsequently easily removing them from the skin. Furthermore, the tape should have high water vapour permeability to avoid skin damage because it is directly attached to the skin, in which high water vapour permeability can promote wound healing.
Conventionally, the adhesive tape has the pressure-sensitive adhesive (PSA) coated onto an entire surface of the backing layer. Thus, conventional tapes are disadvantageous in terms of low water vapour permeability, due to the coated adhesive per se, regardless of the water vapour permeability of the backing layer. That is, even though a backing layer having high water vapour permeability is used, the adhesive coated on the entire surface of the backing layer may prevent water vapour permeation, whereby the water vapour permeability of the tape is reduced.
The user of the adhesive tape may come into contact with water. Hence, water or liquid resistance is required to protect the wound or medical appliance.
Dot-shaped patterns of pressure sensitive adhesives (PSA) coated on backing film allow increased vapour permeability at the areas which are not coated. However water infiltration or leakage is possible via the interconnected uncoated areas or channels, which are defined between the non-interconnected dots of a dot-shaped adhesive pattern.
Specifically, dot-coated parts are discontinuously formed, that is, the coating parts are not interconnected, whereby water is infiltrated between the coating parts. Such infiltration of water leads to maceration of the skin, which is harmful to the wound.
U.S. Pat. No. 6,171,648 discloses a backing material with a partial self-adhesive coating.
A net shaped adhesive on an unperforated backing film is known. Such coating also has the advantages of the dot coatings, with the connected net of adhesive being able to form barrier against leakage. The permeability of the net coating is limited by the area without adhesive and the permeability of the backing film.
WO 2005/028581 discloses a medical adhesive tape, having high water vapour permeability and water resistance, characterized in that a pressure-sensitive adhesive is coated on a base sheet to form a net-shaped structure. As such, the net-shaped structure includes a continuous rectilinear form having square pores, a continuous curvilinear form having slanted square pores, a continuous form having circular pores, or combinations thereof. The adhesive tape includes surgical tape and plasters serving to adhere medical appliances, rolled bandages, wound dressings, transdermal absorbents, etc., to the skin, and can permit the passage of a gas through a plurality of non-coating parts to have high water vapour permeability, and simultaneously have water resistance and sufficient adhesion through a continuous net type coating part.
The adhesives used in the known methods of manufacturing are often solvent based. Furthermore, a drying or curing step usually follows the pattern formation.
Most of the known coating methods can only coat one uniform thickness at one time.
Often there is some waste from the coating process in the equipment for making the patterns.
Typically the release liner totally encapsulates the adhesive.
Typically the net shaped adhesive known from the prior art is uniform in pattern, size and shape.
According to most of the known methods, the pattern is formed first, thereafter cured or dried, and finally followed by laying on a release liner.
Often the known methods of making net coatings involve coating a flowable mass which is subsequently made form-stable, e.g. by gelation. The interval between the coating and form-stable stage allows the adhesive mass the opportunity to flow. Especially for less viscous materials such as materials having a viscosity below 1 Pa·s, this flow out will mean that more of the backing film is covered by the adhesive than is intended. As the adhesive free area of backing film is reduced, the permeability of the adhesive layer is also reduced.
The net pattern produced by known methods is often such that the base surface/area in contact with the backing film is larger than the top surface/area, at the opposite end of the base area, due to flow. This reduces the adhesive used for contact with skin, and increases the adhesive covering the backing film thereby helping to increase permeability.
EP 5 532 275 discloses a non re-enforced and non-adherent dressing hydrophilic gel. The gel is manufactured by applying an aqueous solution to a mould defining a pattern of interconnected grooves and subsequently drying the solution in the mould to form the dressing.
DE 29 00 319 discloses a punching apparatus for making coiled bands with adhesives.
EP 0 437 916 discloses a method for producing an air-permeable adhesive tape by forming a layer of a solution on a substrate, the solution comprising an adhesive in an organic solution; applying water drops on said layer and evaporation the organic solvent contained so as to form an adhesive that contain water drops and finally evaporating the water. However, it will be appreciated, that the size and distribution of the water droplets are difficult to control.
As use of organic solvents is associated with environmental and health problems, it is an object of a preferred embodiment, to provide a method in which the adhesive does not contain organic solvents.
US 2005/0228329 discloses polymer material which in order to be gelled must be cooled down from a heated state. It will be appreciated that such heating and subsequently cooling is time consuming and accordingly, it is an object of a preferred embodiment of the present invention to provide a less time consuming method/process.
Often a release liner is added afterwards when the adhesive gel is sufficiently cold, for handling purposes, e.g. rolling up. The liner, due to pressure exerted from it, may affect the final surface shape of coating depending on how far into gelation the adhesive has reached at the point of application of liner onto the coated adhesive.
A dressing normally contains a central part comprising an absorbent core.
If the absorbent core is directly attached to the middle of the coated backing layer, the adhesive area between the absorbent core and adhesive layer is largely wasted as it is not used for adhering to the skin as intended. The adhesive, though formulated for good properties for skin contact, may not have the optimal properties for attaching the absorbent core. For attachment of the absorbent core, a cheaper or more effective adhesive or attachment method may be used.
An exposed absorbent core on a backing film requires good anchorage to the backing film, especially when wet and heavy due to being soaked with exudate. By good anchorage is meant that absorption of moisture does not cause the absorbent core and the backing film to delaminate.
An exposed absorbent core surface facing the wound side maximises the exudate absorption when in place. However, longer term placement (such as for a period longer than 3-5 days) on the wound may lead to growth of tissue of the healing wound onto the absorbent core surface or more difficult removal, which in turn irritates the wound.
To overcome the removal problem, contact layers of less adhering nature are known. These contact layers are often thin films or gel layers having perforations to expose the absorbent core.
EP 633758 discloses an absorbent wound dressing having a layer of hydrophobic silicone gel which is intended to lie against the wound surface when the dressing is worn. A layer of carrier material carries the gel layer and affords the requisite strength thereto. An absorbent body is placed on that side of the carrier material and gel layer which lie distal from the wound surface in use. The carrier material and the gel layer have mutually coinciding penetrating perforations at least within the region of the absorbent body. A fluid barrier layer is provided on that side of the dressing which lies distal from the wound surface in use.
Another function of the contact layer may be to support and hold the absorbent core in position.
There is a need to simplify and improve the processes of making net patterned adhesive layer and especially for making dressing construction with different patterns at different parts of the same net patterned adhesive layer. There is a need to maximize the contact area to skin but minimize the coverage of the backing film. There is also a need to reduce the flow out of the edges of such coated patterns